Methods of preparing reference patterns for pattern recognition systems



350-320 SR gEARCH ROOM OR 304989191 I March3, 1970 w. E. DICKINSON3,493,191

METHODS OF PREPARING REFERENCE PATTERNS ,FOR PATTERN RECOGNITION SYSTEMSOriginal Filed May 26, 1961 2 Sheets-Shoot 1 PROPERTY IDENTIFICATIONcmcung I28PERTY I?) ONE-SHOT I A umvmrwo I I2 I8 PROPERTY ONE-SHOTMEASURING n umvmmmfi I VOICE INPUT ,qggggggg ONE-SHOT SIGNALS QRCUH'MULTIVIBRM I i h 20) i H ONE-SHOT MEASUR'NG MULTIVIBRATOR I $5.1" I IONE-SHOT MEASURING l y I .0 warm r L.

52 49 M7 FIG I one-sum ONE-SHOT f? comm AMPLIFIER moms l mvla mnvmrms vsvmcn 54 MINIMUM m commsou cmcun PROPERTY PROPERTY 48 I D l I I B I 49INVENTOR WESLEY E. DICKINSON BYQ a JTO AND GATES fl I0 TIMING CONTROLCIRCUITS Q ATTORN S March 3, 1970 METHODS OF PREPARING REFERENCEPATTERNS FOR PATTERN RECOGNITION SYSTEMS Original Filed May 26, 1961 2Sheets-Sheet 2 w. E. DICKINSON 3,498,191

SANE WORD SPOKEN REPEATEDLYBY SAME OR DIFFERENT PERSONS DIFFERENTPROPERTY MEASUREMENTS MADE SIMULTANEOUSLY LIGHT PATTERNS GENERATED FIG.5 CORRESPONDING T0 PROPERTIES FILM SUCCESSIVELY EXPOSED T0 LIGHTPATTERNS FOR EQUAL TIMES FILM DEVELOPED so THAT TRANSMISSIVITY ISMATCHED TO THE DESIRED CHARACTERISTEIC SCALE PROBABILITY or OCCURRENCEWVENTOR- WESLEY E. DICKINSON United States Patent 3,498,191 METHODS OFPREPARING REFERENCE PAT- TERNS FOR PATTERN RECOGNITION SYSTEMS Wesley E.Dickinson, San Jose, Calif., assignor to International Business MachinesCorporation, Armonk, N.Y., a corporation of New York Originalapplication May 26, 1961, Ser. No. 112,939, now Patent No. 3,234,392,dated Feb. 8, 1966. Divided and this application May 20, 1965, Ser. No.457,377

Int. Cl. G03b 41/00 US. Cl. 951 1 Claim ABSTRACT OF THE DISCLOSURE Amethod of preparing separate areas within a reference pattern elementfor automatic recognition of manifestations of intelligence such asspeech repeats the given manifestation, such as spoken word,'a number oftimes for sampling purposes. In each repetition, selected properties orspeech characteristics in the manifestation being analyzed are monitoredto ascertain their presence or absence in the repetition. For each suchreading, a light is flashed for a selected interval to expose a chosensegmental area of a reference pattern film, which then effectivelystores the cumulative total of the number of exposures. The film isdeveloped in a non-linear manner to give complete reference patterncomprising a number of areal divisions, in each of which the number ofexposures for each individual area are weighted so as to enhance therecognition function, as by representing the logarithm of theprobability of occurrence of the property.

This invention relates to the recognition of meaningful visual and auralmanifestations, and more particularly to processes for preparingreference patterns for the recognition of speech.

This application is a division of my prior application entitled PatternRecognition Systems, Ser. No. 112,939, now Patent No. 3,234,392, filedMay 26, 1961.

The highly complex sounds of human speech and the complex patterns ofprinting and handwriting illustrate the difiiculties involved inautomatic pattern recognition. Currently, in order to supply data tomodern high-speed electronic systems, it is usually necessary to prepareinput information specially, as by punching cards, encoding magneticcharacters on a sheet, or punching paper tape. These methods ofconverting input information to machine language are time consiuming,expensive, and subject to error. Many attemtps are currently being made,therefore, to devise systems for the automatic recognition of speech,print and handwriting. With such pattern recognition systems dataprocessing operations can begin directly with information derived fromthe predominantly used modes of communication,

So many variations are encountered in speech and in writing, however,that complex compensating mechanisms have had to be'adopted inrecognition equipment. The human mind, of course, can readilydistinguish the meaningful content of most communications despite theconcurrent presence of what may be regarded as noise effects. As oneexample, handwriting is so highly individual that an expert can oftenidentify the source even where an uncharacteristic style has beenattempted by the writer. The same message, handwritten by a number ofdifferent persons, can be distinguished except where the writing is sounreasonably bad as to be illegible.

The recognition of speech poses subtler and additional problems,primarily because of the transitory nature of speech, and the greaternumber of variations possible. Meaning is derived by a listenerfromvwhat is said and also from the manner in which it is said, despitedifferences in loudness, speech rate, intonation, pitch and infiection.The problems involved in the recognition of the primary informationcontent of speech are nonetheless not insuperable, and marked advancestoward automatic recognition have been made by electronic devices whichrespond to certain energy and frequency distributions in sound which cancharacterize particular spoken words or subunits of words. It hasseparately been shown that many spoken sounds, which may or may notcorrespond to phonetic syllables, may be reliably identified ordistinguished through the existence of other selected properties.Clearly, as many of these different properties should be used as canreasonably be accommodated by a system without involving meaninglessredundancies. The importance which can be attached to differentproperties and characteristics is, however, highly variable. Certaincharacteristics may be very reliable indicators when used in one word,but be quite ambiguous and indefinite as they occur in a different word.The various properties must therefore -be weighted, and each combinationof properties must be considered as a whole in identifying themanifestation which the combination represents.

This determination of the interrelationship between the differentidentifiable properties of a manifestation is a necessity for anyversatile recognition machine. In providing a reference pattern orpatterns for recognizable manifestations it has sometimes been thepractice to use a number of repetitions of each manifestation, and toadditively combine the effects of the repetitions. As one example,amplitude distributions with time in a spoken word may be used togenerate correspondingly varying curves in rectangular coordinates. Thecurves then are superimposed on each other to provide an aggregaterepresentation which accounts for minor variations. This technique,however, limits the number of properties which can be considered and isnot readily repeatable. A different technique which is used is toprovide calculated values for each property in a manifestation, but thisrequires a tedious collection and reduction of input data and is timeconsuming and expensive even if a high speed data processor is used. Theprocesses heretofore used for gathering the necessary statistics havetherefore been complex and prohibitively costly for use in practicalapplications.

It is therefore an object of the present invention to provide animproved process for preparing a reference pattern for use in automaticrecognition machines.

Methods in accordance with the invention utilize successive steps in thepreparation of a recognition pattern by which elemental areas of therecognition pattern are caused to have light transmissivitycharacteristics which vary according to the logarithm of the probabilityof occurrence of a given property in the manifestation i.n volved.

In a specific example of methods in accordance with the invention,reference patterns for automatic recognition machines are prepared byphotographic means under control of separate property measurementelements. At least a pair of lights is employed for each measurement tobe made. As a given word is spoken successively by a person, or bydifferent persons, a selected one of each of the light sets,representing either the existence or the absence of the selectedproperty, or one of a group of conditions, is flashed for apredetermined duration. The variations in the manner in which the wordis spoken, and in the resultant combinations of lights which areflashed, cause different exposures of the various areal divisions of theproperty reference pattern on the film, as the film is held fixed in aposition corresponding to the sample word being entered. The film isthen developed so that the opacity of a given areal division isproportioned to the more particular description of a preferredembodiment of the invention, as illustrated in the accompanyingdrawings. FIG. 1 is a combined block diagram and perspective view of onearrangement of a manifestation recognition system in accordance with thepresent invention;

FIG. 2 is an enlarged side view of a fragment of a reference patternemployed in the arrangement of FIG. 1; FIG. 3 is a plan sectional viewof a portion of the arrangement of FIG. 1;

FIG. 4 is an enlarged idealized representation of elemental referencepattern areas on the reference pattern of FIG. 2;

FIG. 5 is a block diagram showing successive steps which may be employedin methods in accordance with the present invention, and

FIG. 6 is a graphical representation of one manner in which a referencepattern may be processed in methods in accordance with the invention.

The system which is here described is merely one example ofmanifestation and pattern recognition systems,

but is particularly meaningful because it satisfies very criticalrequirements. Specifically, the example described is a speechrecognition machine which is intended to recognize certain words out ofa selected but nevertheless extensive vocabulary. It is intended toidentify each spoken word of the vocabulary, irrespective of normal andreasonable variations in the speech of an operator or differentoperators, and to do so with sufficient rapidity for the input speech totake place at normal and convenient rates. Other examples of differentkinds of pattern recognition might also be given, including recognitionof printed and handwritten characters, as systems in accordance with theinvention require only that pattern properties be identified.

Referring now to FIGS. 1, 2 and 3, electrical signal representations ofa spoken word as derived by a microphone and amplifier system (notshown) are provided by system. Because of the complexities involved inspeech recognition, many different types of measurements have beenevolved and conceived, and systems in accordance with the presentinvention are amenable to the use of most of these differentmeasurements, even though the measurements themselves may be of whollydifferent types.

Early work in the field of speech recognition used frequency and energydistributions with time as a basis for distinguishing sound patterns.Sounds which are voiced,

that is sounds which emanate primarily from resonance of the vocalcords, can be characterized by the existence of frequencies ranging upto several thousand or more cycles per second. The voiced sounds, forexample, include most of the vowel sounds. It has been shown, moreover,that the different voiced sounds in a single multiple syllable word willoften follow characteristic energy and frequency distribution patterns.Words are recognized by comparison of sample patterns to previouslyprepared standard patterns representative of such distributions. Inthese as well as in many other circuits, some form of normalizing isusually employed, so as to compensate for the different speech rate,amplitude and frequency characteristics of different individuals.Whether normalizing is used or not some selected time base is generallyadopted.

The frequencies which characterize the voiced sounds are ascertainableeven though the oscillations are of relatively brief duration and aredamped by the human speech mechanism. The so-called frictional sounds,however, are much more noise-like in character and are typicallydistinguished by much higher frequency components which may beidentified by appropriate filters. By closer analysis, various voicedand frictional sounds may be distinguished and a vocabulary ofrecognizable words built up, based upon the reference patterns.

Another more recent and potentially much more powerful technique doesnot require either normalization or the adoption of a time base, butsegments each word in time in accordance with certain transitions in theword itself. According to this technique, voiced speech is very reliablyidentified by an asymmetry between components of opposite polarity inthe complex multifrequency speech wave. Furthermore, by varying thephase relationship of these multifrequency components, the asymmetrycharacteristic changes in certain ways which distinguish the differentkinds of voiced (or partially voiced) sounds from one another. Usingthese relationships, as well as the recognition of various frictionalsounds, there are established machine syllables on which may be based alogical notation having both quality and time significance. Wordrecognition is then accomplished by comparison of generated sequencesagainst stored sequences in appropriate switching arrangements. The useof machine syllables requires, when used in this way, considerablediscrimination against noise as to each property. Greater reliabilitymay be gained by increasing the number of properties. Yet, as describedabove, this entails a great deal of work in order to get best efficiencywith a particular operator, and extensive changes may be needed forother operators. The present invention permits these differenttechniques and properties to be used together in a manner which allowsthe proper weight to be attached to each property.

The term property measuring circuit therefore should be taken to meanany type of measuring circuit which provides a meaningful output signalfor pattern and manifestation recognition. Preferably, each of thesecircuits should include a threshold circuit or arrangement capable ofproviding a selected signal to noise ratio. Threshold circuits as suchneed not necessarily be employed, however, because the present systemautomatically compensates for probability factors. Here it should benoted that while only simple yes-no decisions are made here as to thevarious properties, the decisions may involve a greater number ofalternatives. Energy content at a given frequency may be measured, forexample, and different property indications given for each of a halfdozen different levels. Output signals from each of the propertymeasuring circuits 11-15 trigger different ones of a group of associatedone-shot multivibrators circuits 17-21 respectively. The one-shotmultivibrators 17-21 provide, when triggered, like pulses which are ofselected duration and amplitude. In this arrangement, these pulses lastfor at least two cycles of operation of the associated reference patternmechanism. The pulses control the operation of separate switches 2226respectively which are coupled to a regulated power supply 28 (shownschematically). The switches are arranged, in their normal state, tocouple the power supply 28 to a first one of two output terminals. Inthis normal state, the switches indicate the absence of the property towhich the associated measuring circuit 11-15 is responsive. Undercontrol of the output signal from the associated one-shot multivibrator17-21, however, each switch 22-26 couples the power supply 28 to theopposite output terminal for the selected duration. Signals on theseoutput leads denote that the specific property has been detected in thevoice input signals. For convenience, the properties are designated A,B, C, D and E respectively, and the presence of the property isindicated by A while the absence of the property is indicated by X. Ifmore alternatives were used for any property a corresponding number oflights and an appropriate trigger system would be used.

The AE signals control the generation of light patterns in a wordselection device which uses a variable opacity reference disc 30 havinga transparent body. The reference disc 30 and associated lightgenerating, light collecting and detecting elements are contained withinan enclosure (not shown) which shields the operative elements fromambient light and where necessary from interference between the variousindependent light sources. The disc 30 rotates on a central shaft 32which is driven by a constant speed motor 33.

Various property reference patterns 35 are disposed along radiallyextending segments about the circumference of the disc 30. Each radialsegment is further divided along the radial direction into small areaswhich vary in opacity in a predetermined manner. Each radial segmentalso includes a word identification pattern 37 which serves to generatea desired digital code representative of the word with which theproperty pattern 35 is associated. An index pattern 38 is also disposedat one selected circumferential position about the disc 30.

These details may be better understood by reference to the view of FIG.4 in addition to FIGS. '2 and 3. FIG. 4 represents a fragment, ingreatly enlarged form, of a portion of the reference disc 30. Theadjacent property patterns 35 are innermost relative to the disc 30, theword identification patterns 37 are next, and the index pattern 38 is atthe outermost position, although this order may be shifted or reversed.Those skilled in the art will recognize that the disc 30 is merely oneexample of a cyclic member which moves so as to cause successivepatterns to scan past a given axis. Each property reference pattern 35has a pair of variable opacity areal divisions for each of the fiveproperties, A, B, C, D and E which are used in this example. The arealdivisions which make up each pair represent the presence and absence ofthe given property. When the number of possibilities for a givenproperty is greater than two, the areal divisions are made to correspondin number. Each areal division has an opacity which is proportional tothe logarithm of the probability that a given property condition willoccur in the word which the property pattern represents. The wordidentification patterns 37, however, are used to generate a binary codeand so consist of areal elements which are either of maximumtransmissivity or of maximum opacity. A nine binary digit code isillustrated. The circumference upon which the index pattern 38 ispositioned is entirely transparent except for the index pat-' Thesignals A-E and K-E which denote the presence and absence of the variousproperties for yes-no decisions control different ones of a set of likelights 40. In order to have high density stora e of the data representedby the patterns on the drum 30, these lights 40 are preferably verysmall, and may be neon elements, electroluminescent elements, or thelike. It is particularly to be noted that all the lights 40 should havelike characteristics, including intensity, aging and responsecharacteristics. A single light 41 is employed in conjunction with theword identification patterns 37 and the index pattern 38, but this light41 is shielded from the property patterns 35. The lights 40, 41 arepositioned along a selected fixed radial axis relative to the drum 30,and thus disposed so that the patterns on the drum successively scanpast during rotation. Each of the lights 40 is aligned with a differentareal division of the property patterns 35.

A light collector system is employed adjacent the property or referencepatterns 35, so that light beams directed through the disc 30 from thelights 40 impinge similarly on a single photosensitive element 43, hereshown as a photocell, although any photosensitive mechanism havingsufiicient sensitivity may be used. Separate photosensitive elements 45,appropriately'shielded (see FIG. 3) so as to receive only light passingthrough a corresponding digital valued area, are employed in conjunctionwith the word reference pattern 37. Each of these elements 45 is coupledto an associated one-shot multivibrator 47, the

pulse groups provided at the output terminals of the oneshotmultivibrators 47 thus forming in binary code the successive wordsrepresented on the drum 30 as they pass the elements 45. At the radiusof the drum 30 containing the index pattern 38 position there isemployed a single photosensitive element 48 coupled to a one-shotmultivibrator 49 and providing pulses which mark the passage of theindex pattern 38 through the fixed axis.

An amplifier circuit 50 coupled to the photosensitive element 43 appliessignals generated thereby to a switch 51 which is operated by a timingcontrol circuit 52. The timing control circuit 52 operated duringsuccessive cycles of the disc 30 to switch the signals from thephotosensitive element 43 either to a minimum signal storage circuit 54or to a comparison circuit 55 on alternate cycles of the disc 30.Because the signal representative of a word need not be applied tosynchronism with the rotation of the disc 30, the timing control circuit52 is utilized to insure that at least one full rotation of the disc 30is provided for storing the minimum signal derived from the referencepattern mechanism, and that another full rotation is then provided foridentification of the word by comparison of the transitory signal fromthe element 43 to the stored signal level. The timing control circuit52, therefore, responds to the pulse from the one-shot multivibrator17-21 and to the index pulses from the one-shot multivibrator 49 tocontrol the switch 51 so that the signals from the amplifier 50,following a pulse from a one-shot multivibrator 17-21, are provided tothe minimum signal storage circuit 54 during the remainder of therevolution, and during the next complete revolution of the disc 30. Uponcompletion of the full revolution of a disc 30, theindex pulse appliedto the time control circuits 52 actuates the switch 51 so that thesignals derived from the photosensitive element 43 are applied to thecomparison circuit 55. Effectively, therefore, the timing controlcircuit 52 is a triggered bistable device.

The minimum signal storage circuit 54 may be merely a capacitive circuitwhich is charged to a level determined by minimum excitation of thephotosensitive element 43. The comparison circuit 55 is an amplituderesponsive circuit and provides an output signal, at the one point inthe second full rotation of the disc 30 at which the stored signal andthe transitory signal are substantially equal.

When an output signal is provided from the comparison circuit 55, adigital code value is also derived from the word identification patterns37. The pulse groups from the one-shot multivibrator-s 47 are applied toAND gates '57 and are gated through the AND gates 57 under control ofthe output signals from the comparison circuit 55.

The manner in which this system automatically takes into account theprobability of specific proper conditions may be better understood byreference to FIG. 4. The five different yes-no properties A-E which hereserve as the basis for word recognition are represented by the lighttransmissivity characteristics of different pairs of areal divisions ona property reference pattern 35 on the disc 30. Light transmissivityvariations which may exist for different words are shown in idealizedand enlarged form. These variations are represented as opacitygradations against a transparent background with the highest degree ofopacity corresponding to the highest probability to be encountered. Itwill be recognized that the light transmissivity variations need not berepresented by differences in opacity, but may also be represented bydifferences in the light reflectivity of shaded areas. The opticalsensing system which is employed may similarly assume a number ofdifferent forms, although the arrangement shown in FIGS. 1-4 ispreferred.

Each of the paired variable opacity areas corresponding to a givenproperty is meaninglyfully used in establishing the interrelationshipbetween the properties found to exist in a given word. Where there is anextremely high probability that a property will be present, thecorresponding one of the paired areas (designated the yes area in FIG. 4to denote the existence of the property) is highly opaque, and hererepresented as a darkened area. The other area, designated no to connotethe absence of the property, then has a degree of opacity which iscomplementary on a logarithmic scale to the opacity of the yes area.Such a condition is represented in FIG. 4 by property A. Where thesignificance of a property as applied to a given spoken word is lessdefinite, the opacities of the yes and no areas are both intermediatethe extremes. A condition in which the yes is slightly more probablethan the no is shown for property B. Property C, in which the no area isslightly more opaque than the yes area represents the converse, in whichit is more likely that the property will be absent, although there isstill some probability that the property will be found to exist.Properties D and E, in which the no areas are strongly opaque, areproperties which are unlikely to be found to exist in conjunction withthe given word.

With a set of areal divisions greater than two in number only one of theareal divisions need have an opacity gradation. With more than twoalterativies only positive indications of the presence of a property aregiven.

Now, as described below, the gradation of the opaque areas is inaccordance with the logarithm of a probability and not in accordancewith the probability itself. If there is a nine out of ten chance that agiven property will be found to exist (or be absent) the opacity of thecorresponding area is not 90%, but the appropriate logarithmic valuethereof. 7

This arrangement, therefore, does not rely directly upon the yes-no orone out of a number decisions in the property measuring circuits 10, butinitiates a combined digital and analog decision making sequence byactuating the lights 40 adjacent the property patterns 35 in a patterndetermined by the spoken word sample. This light pattern is held for afirst complete revolution of the reference disc 30, during which thevarious property patterns 35 scan across the axis of the'lights 40 insequence. All of the areal divisions of each property pattern 35 passacross the set of lights 40 at the same time. In the intervals betweenregistration of the successive property patterns 35, there is maximumlight transmission through the disc 30 because of the transparentbackground of the disc 30, and a maximum signal level is provided by thephotosensitive element 43.

The first complete revolution of disc 30 may be referred to as a storagecycle, because during this revolution the signals provided from thephotosensitive element 43 are applied through the switch 51 to theminimum signal storage circuit 54. The minimum signal level is derivedwhen the pattern in which the lights 40 have been excited results in theleast transmission of light through the disc 30. On the next revolutionthe transistory signal from the element 43 is compared to the storedsignal, and the comparison output signal is provided at the instant whenthe property pattern 35 for the most likely word crosses the axis. Atthis time the word recognition pattern is read out through the AND gates57.

Those properties, such as properties B and C in FIG. 4, which haveintermediate opacity gradations prevent the stored signal from everapproaching absolute zero. This would signify that a word had beenrecognized with absolute certainty which is, of course, not realistic.On the other hand, it mayintuitively be seen that the use of logarithmicfactors for the different properties materially enhances accuracy andreliability. For other words the best match, whether or not the inputword is included in the system library.

One example of the way in which a reference pattern may be preparedphotographically in accordance with the invention is illustrated in FIG.5. The mechanism which is used may be essentially that shown in FIGS. 14except that the light sensitive material of the reference member is, ofcourse, initially unexposed and undeveloped. The light sources to whichthe light sensitive material is exposed are actuated for preciselycontrolled intervals in response to identification of the variousproperties. The property patterns may be imposed directly on the discitself, after application of a light sensitive film, or on separate filmframes or plates from which the patterns may be transferred mechanicallyor by photographic means to a disc or other reference member. Anappropri ately configured image mask may be used adjacent the lightsensitive member so that the light spot outline is sharply defined andthe exposure intensity is uniform across the entire illuminatedarea.Furthermore, the intensity of each of the illuminating sources, and thedurations for which they are excited, are the same for each exposure,both as between different lights, and as to successive exposures.

With this mechanism, property patterns as to reference words may beestablished by having an individual speak the same word a number oftimes in succession, or by having a number of individuals speak the sameword separately at different times. The choice as to the manner in whichthis is done will largely be determined by the ultimate use of the wordrecognition machine, and whether it is to be employed with a specificselected operator or a number of different operators. As each word isspoken, the property measurement circuits respond to the electricalsignals representative of the word by identifying the existence orabsence of the selected properties in the word, with yes-no decisions,or by identifying specific conditions of a given property having morealternatives. As described above, the property measurement circuits mayrespond to frequency-time distributions, particular frequencycharacteristics, asymmetry characteristics and a wide variety of otherselected information, such as the occurrence of more than one voicedsound in the selected word. Each time a given word is spoken, theproperty characteristics are indicated by the excitation of one of thepair or set of lights which is used for the property. The inevitabledifferences in modulation and expression of the same word will usuallyresult in different light patterns during at least some of thesuccessive enunciations. As reference samples are accumulated, however,the areal divisions for the given properties come to represent, throughextent of exposure, the probability that the specific propertyconditions will occur in the word. Because of the highly variable natureof speech, few indications will be invariant, and property conditionswill usually be identified to an intermediate degree. Each of theelemental areas of a pair or set corresponding to that property will,therefore, be exposed somewhat, in a proportionality dependent upon thenumber of times each of the associated light sources has been actuated.

It should be noted that there is a relationship between the probabilityvalue which can be attached to a given than the one correct word thelight transmitted will usureading and the threshold level at which theassociated measurement circuit is set. If, for example, a high amplitudesignal is required to exceed the threshold level and to provide anoutput signal indicative of the existence of a property, there should bea sharper contrast between the yes and no areas of the pairs for themajority of properties. In effect, the no areas will be accentuated.This limits the usefulness of the individual properties, however. Theselection as to the threshold level must, therefore, be made relative tothe total number of properties which are available and to the totalnumber of readings which it is desired to use in generating the lightpatterns for exposure.

Finally, in accordance with the invention, the exposed film is developedin a controlled fashion. The develop ment is such (see FIG. 6) that theopacity (more generally, the density) of a given area is madeproportional to the logarithm of the probability of the occurrence of acondition. The number of exposures of a given areal division is ameasure of the probability of occurrence of the condition which thedivision represents. The photochemical change in the sensitized filmwith exposure is such that, in combination with the development process,the desired logarithmic variations is closely approximated.

As shown in FIG. 6 the normal development characteristic of the film,when exposure is plotted against the resultant opacity, is somewhatS-shaped, but approximates the ideal logarithmic curve for brief andintermediate exposure times. These S-shaped curves vary in slope,depending upon the development time which is used. At peak values,opacity levels off, so that the maximum opacity must be selected to bewithin the region of the ideal curve. The position of the curve may bevaried along the abscissa by selecting the individual exposureintervals. Then, the development may empirically be controlled so as tosimulate the logarithmic function. If desired, samples exposed underknown conditions may first be developed separately to provide knownstandards for final adjustment.

Among the many advantages which accrue from this process it is importantto note the simplicity by which statistics may be gathered and used todefine extremely complex relationships. Heretofore, close analysis ofthe speech characteristics of one person has had to be made preparatoryto an extensive compilation of a vocabulary. The larger the vocabulary,the more difiicult and time consuming has been the problem of properWeighting of individual factors. With methods in accordance with theinvention, however, directly usable reference patterns are providedwithout the need of complex additional equip ment.

In generating the patterns during the accumulation of reference samplesit may be convenient to use a recording of words in -a specificsequence, and then to sort the word patterns out and actuate the lightsystem.,In this way a complete reference member may be provided anddeveloped at high speed. Or an individual operator may position thereference member and enter successive or repeated reference wordpatterns.

While the invention has been particularly shown and described withreference to a preferred embodiment thereof, it will be understood bythose skilled in the art that the foregoing and other changes in formand detai s may be made therein without departing from the spirit andscope of the invention.

What is claimed is:

1. The method of preparing a reference pattern for speech recognitionmachines, the reference pattern providing a reference vocabulary bystatistically weighted representations of different selected propertiesof speech as they occur in different words, which includes the steps ofsuccessively illuminating sets of areas of a light sensitive film inaccordance with actual identification of the selected properties in arepeated series of each spoken word, such that separate areas areexposed to light for total times in an additive accumulation of thespecific property conditions in the different repetitions of each spokenword, and developing the film to convert the additive accumulations tologarithmically varying gradations in the opacity of the film, with thegreatest opacity being representative of the greatest number ofexposure.

References Cited UNITED STATES PATENTS 1,781,550 11/1930 Kwartin179l00.3 2,590,110 3/1952 Lippel.

3,006,713 10/1961 Klein et al. 346 108 2,519,194 8/1950 Maurer 179-10031X 3,116,963 1/ 1964 Kiyasu v 346-107 3,292,148 12/ 1966 Giuliano340l46.3

MAYNARD R. WILBUR, Primary Examiner L. H. BOUDREAU, Assistant Examiner

